Color developing solutions used to form dye images on silver halide color photographic materials generally contain p-phenylenediamine color developing agents, alkali agents such as sodium hydroxide, sodium carbonate, trisodium phosphate, sodium metaborate and borax, antioxidants such as sodium sulfite and hydroxylamine salts, and development restrainers such as potassium bromide, potassium iodide and 6-nitrobenzimidazole nitrates. If necessary, other components may be contained to achieve special purposes; for example, a color development accelerator such as benzyl alcohol may be used for the purpose of facilitating the penetration of the oxidation product of the color developing agent into oil globules that contain a coupler and are dispersed in an emulsion layer, thereby promoting the desired color formation through the binding with the coupler.
The developing power of the developing solution decreases as silver halide color photographic materials are processed in large amounts and as the oxidation of the developing solution proceeds during storage. Such exhausted developing solution must be replaced partially or entirely so as to maintain the desired range of developing power. Replacement is also made of subsequent processing solutions such as stopping bath, fixing bath, bleaching bath, blix bath and stabilizing bath for the purpose of maintaining their performance. However, part of the developing solution on the photographic material is carried over into the subsequent processing solutions and discarded when the latter are disposed of for replacement. As a result, the waste color developer and other photographic processing solutions contain various additives such as p-phenylenediamine developing agent in fairly high concentrations. In particular, the p-phynylenediamine developing agent has BOD (biochemical oxygen demand) and COD (chemical oxygen demand) higher than the values tolerated by antipollution laws such as the Water Pollution Prevention Act and Sewerage Law, and may cause environmental pollutions if it is discharged directly into sewerage and other watercourses.
In order to avoid this problem, the photographic processing solutions containing the p-phenylenediamine developing agent must be discharged into sewerage and other watercourses after the developing agent and other pollutants are separated or recovered from the processing solutions or otherwise rendered harmless. It is therefore necessary to develop techniques effective for achieving this purpose. On the other hand, the p-phenylenediamine developing agent is expensive and discarding the separated and recovered p-phenylenediamine is not desired for economical reasons. It is therefore advisable to put the separated and recovered p-phenylenediamine compound to another use as a color developing agent.
Various methods have been proposed for separating the color developing agent from photographic processing solutions discharged from such steps as color development, fixing, bleaching and stabilizing. U.S. Pat. No. 3,884,983 shows a method of separating and removing a certain compound from a processing solution by contact with activated carbon. U.S. Pat. No. 2,358,053 shows a method of extraction with an organic solvent such as kerosene. Japanese Patent Publication No. 33698/73 shows a method of separating and recovering the developing agent and other components by salting-out the developing solution with a salt such as sodium sulfate. U.S. Pat. No. 3,253,920 proposes a method of recovering the developing agent dissociated with the aid of an anion exchange resin. Japanese Patent Application (OPI) No. 82235/77 (the symbol OPI as used herein means an unexamined published Japanese patent application) shows a method of separation and recovery using a styrene-divinylbenzene copolymer. Japanese Patent Application (OPI) No. 50737/78 shows a method of separating the developing agent and other components from a photographic processing solution by contact with a methacrylate polymer.
However, these methods have various defects from a practical viewpoint. The first method using activated carbon features ease of operation and high ability to separate organic matters from the aqueous solution. However, selective adsorption of a certain organic matter is not possible. Furthermore, the activated carbon has such a strong adsorbing power that the organic matter cannot be easily desorbed from the carbon and requires complex and expensive separation and purification procedures. The second method that depends on extraction with an organic solvent uses a large quantity of inflammable organic solvent which is not only toxic but also presents a great fire hazard. Furthermore, these solvents are expensive. The third method requires a large amount of salt and is not highly recommendable from an economical viewpoint. In addition, this method salts out all compounds that are hardly soluble, so a complex procedure is necessary for purifying the developing agent and other compounds separated from the salt solution. The fourth method is also not highly practical because the anion exchange resin is very low in its efficiency of removing the p-phenylenediamine developing agent having a low degree of dissociation. The fifth method that uses a styrene-divinylbenzene copolymer and the sixth method using a methacrylate polymer to adsorb a certain compound in the photographic processing solution experience a gradual decrease with time in their ability to remove the certain compound. Furthermore, a large amount of strong acid is used to regenerate the resin adsorber or an organic solvent such as methanol must be used for desorption purposes. However, the use of strong acids and organic solvents is not recommended for safety reasons.
In addition to these individual problems, the prior art methods have one common defect: Recycling of the separated and recovered photographically valuable compound, in particular, p-phenylenediamine color developing agent, requires a complex process involving concentration, crystallization, precipitation and filtration or extraction with an organic solvent, and this is practically beyond the ability of commercial laboratories.